Dehydrogenation of hydrocarbons



Patented May 10, 1949 DEHYDROGENATION OF HYDROCARBONS Carllsle M.Thacker, Highland Park, lll., assignor to The Pure Oil Company, Chicago,lll., a corporation of Ohio No Drawing. Application December 26, 1942,Serial No. 470,302

3 Claims.

more carbon atoms in the molecule suchas ethane, propane, butane orcorresponding oleflns, such as butylene, as well as higher boilinghydrocarbons such as hexane, heptane and octane may be dehydrogenated bycontacting the same at temperatures within the range of 350 to 750 C.with activated alumina oi commerce impregnated with an oxide of a metalof the second group of the periodic table selected from the groupconsisting of beryllium, magnesium and zinc. The activated aluminacontemplated in my invention may be prepared by precipitatingtri-hydrate from an aluminate solution and calcining the precipitate attemperatures of 300 to 800 C., all in accordance with the method setforth in the patents to Barnitt 1,868,869 and Derr 2,015,593. Although Ihave specified activated alumina of commerce, any activated aluminawhich has substantially the same physical and chemical characteristicsor catalytic activity as activated alumina of commerce may be used.Activated alumina" of commerce has approximately the following chemicalconstitution:

Per cent by weight Silica 0.07 Ferric oxide... 0.05 Sodium oxide 0.46Aluminum oxide 89.02

Water, balance.

Upon spectroscopic analysis activated alumina will show the followinglines with the comparative intensities indicated:

Sodium 0.6+ Titanium 3 Gallium 1 Silicon 4 Iron 5 heating the mixturewith frequent stirringuntil almost dry and then completing the dryingslightly above the boiling point of the water. The dry catalyst is thendecomposed by contacting it with air at a higher temperature, not above800 C., in order to convert the metal compound to oxide. Just prior touse, the catalyst is heated with hydrogen or inert gas at elevatedtempera-' ture for a prolonged period of time and is then ready for use.

The following examples represent methods of preparin catalysts inaccordance with my invention.

Example 1.36.7 grams of beryllium nitrate (Be(NO:) :.3H2O) weredissolved in 225 cc. of water and cc. of concentrated nitric acid. Thissolution was added to 8-14 mesh activated alumina of commerce which hadpreviously been heated for 2 /2 hours to 200 F. The mixture was thenheated on a water bath with frequent stirring until almost dry and thendecomposed in a current of air in which the catalyst was graduallyheated over a period of 4 /2 hours from 20 to 186 C., 13 hours from 186to 276 C., 3 hours from 210 to 400 C., and then for 5 hours at atemperature slightly" above 400 C.

Example 2.-58.3 grams of zinc nitrate Zn(NO3)z.6I-I2O were dissolved in250 cc. of water. This solution was added to 400 grams of 8-14 meshactivated alumina of commerce which had been heated in an electric ovenfor 2 hours at C. The mixture was thoroughly stirred and evaporated to asmall volume over a small Bunsen flame and finally dried in an electricoven at130 C. The dried catalyst was treated with a solutionconsistingof 300 cc. of water and 30 cc.

of concentrated ammonium hydroxide. After standing for 40 hours thesolution was filtered and the catalyst washed 5 times with 300 cc. perwash of distilled water, and then dried at 120 C.

Example 3.-40.3 grams of magnesium nitrate Mg(NO3) 2.6H2O were dissolvedin 250 cc. of water. This solution was added to 8-14 mesh "activatedalumina of commerce which had been dried for 30 minutes in an electricoven at 130 C. The mixture was frequently stirred while being evaporatedalmost to dryness in the water bath and the drying was completed in theelectric oven at 130 C'. The catalyst was then covered with 6 normalammonium hydroxide and allowed to stand one week. The mixture wasfiltered and washed 6 times with 300 cc. of boilin water per wash afterwhich it was dried in an electric oven at 105 C.

Example 4.16.5 grams of magnesium carbonate were dissolved in excess ofacetic acid making 196 cc. of solution and this solution was used toimpregnate 400 grams of 8-14 mesh "activated alumina" of commerce in thesame manner as used in the preparation set iorth in Example 3 with theexception that the ammonium hydroxide treatment was omitted.

In dehydrogenating lower boiling hydrocarbons higher temperatures aregenerally required than are necessary with the higher boilinghydrocarbons. For example in the dehydrogenation of ethane temperaturesabove 600 C. are necessary to obtain substantial yields, whereas in thecase of butane temperatures of the order of 550 C. will givesatisfactory yields of unsaturated C4 hydrocarbons. If it is desired todehydrogenate a mixture of hydrocarbons the optimum temperature willdepend upon the relative proportions of the several constituents in themixture, but in heated in a heating coil to approximately the desiredreaction temperature before passing the gas through a bed of catalystcontained in a reaction chamber. the temperature of which was maintainedat the desired reaction level by on electric heating element. The runswere all conducted at substantially atmospheric pressure. The catalystused in runs #4 and #5 was purged with nitrogen while the catalyst wasbeing heated to reaction temperature. Fresh catalyst any case wlilliesomewhere between the optimum was used in each run Table Percent iiyPercent By Run Temp. 8 Time After Start hill- Sample Catalyst 00. 1 veMy Length of Run Sample Taken \l'log g sgligt Volu'rgtgield ciency,

1 Nono 050 109 1Hr..30Min 1 m =3 2 a Act. A1 0 Bo 642-647 686 7 Hrs, 14Min 2 Hrs, 23 Min l4. 8 0. 119 85 b 202 1. 649-654 652 7 1111., 1 Min14. 8 0. 106 75 3 (1 Act. A1 0 Zn 685 348 28 Hrs, 39 Min- 20 Hrs., Min13.5 0. 008 77 b 20: 1. 700 360 221311. 37 Min 15.9 0.111 75 4 1 Aztt.A1 0 Mg Q40 347 5 Hrs, 58 Min 4 Hrs, 12 Min 14. 8 0. 106 74 5 l a Act.A1 0 Mg 687 913 8 Hrs., 39 Min 3 Hrs., 67 Min 8. 6 0. 066 80 b 20: l.687 792 8 Hrs, 39 Min 8 Hrs, 21 Min l2. 7 0. 074 60 1 Gas saturated withwater at 0 C.

B Represents increase in volume of reaction gm: over charging gas.

3 of ethane reacting which forms ethylene.

temperatures for the individual constituents. The dehydrogenation may becarried out in conventional apparatus at atmospheric, sub-atmospheric orsuper-atmospheric pressures. However, where it is desired todehydrogenate parafi-lns or olefins to diolefins, sub-atmosphericpressures should be used and/or steam or other inert gas or vapor shouldbe mixed with the charging stock in order to lower the partial pressureof the hydrocarbons to be dehydrogenated. It is preferable to heat thecharging stock to conversion temperature prior to charging it to thereactor containing the catalyst. The reactor is preferably heated tomaintain it at all times at conversion temperature. When dehydrogenatingparaflins to olefins the presence of large quantities of water vaporshould be avoided since water vapor when present in excessive amountslowers the activity of the catalyst although small amounts are notharmful. I have found that gas saturated with water vapor at 0 C. is notharmful whereas the same gas saturated with water vapor at roomtemperature is decidedly deleterious.

In order to demonstrate the efficacy of'catalysts in accordance with myinvention a series of runs were made using ethane containing a smallamount of impurities as the charging gas. The results on these runs aretabulated in the table. No analysis of the gases from run #1 was made.

ethylene yield could not have been more than 3% even assuming 100%efliciency.

In run #2 the catalyst 'used was prepared in accordance with Example 1.The ratio of 20 to 1 indicated for the catalyst is the molal ratio be-75 ratio of activated alumina to metal of 20 to 1,-

important that the temperature of reactivation be kept below 800 0.,since temperatures above 800 C. permanently injure the catalyst andlower the activity thereof.

The space velocity. which is defined as the ratio of the volume ofcharging gas or vapor per hour The volume of increase of 3% shows thatthe to the volume of the space occupied by the catalyst, may vary overwide limits. I have found space velocity of from to 10,000 to besatisfactory. Generally speaking, lower space velocities give higherrates of conversion, and high space velocities give lower rates ofconversion. The optimum space velocity to be used will be dependent uponthe particular temperature at which the dehydrogenation is conducted,since low space velocities with higher temperatures have a tendency tocause decomposition and carbon formation to occur. The optimum spacevelocity and temperature for obtaining the highest eificiency andhighest yield of the desired unsaturated hydrocarbon can be determinedempirically for each charging stock and catalyst.

Although in the specific'examples previously given the catalysts wereprepared by using a molal this ratio may vary over wide limits. Thecontent of metal, deposited as metal oxide on the activated alumina, mayvary from .596 to 30% by weight of the activated alumina. Amounts ofoxide ranging from 1 to 10% calculated as metal are preferred.

Catalysts herein described, particularly magnesium oxide on activatedalumina are especially useful in the dehydrogenation of butane or buteneor mixtures thereof to butadiene under conditions of sub-atmosphericpressure or at a low butane and/or butene partial pressure.

I claim:

1. The method of dehydrogenating dehydrogenatable hydrocarbons whichcomprises, contacting said hydrocarbons at an elevated temperaturesuitable for dehydrogenation with a catalyst composed of activatedalumina impregnated with beryllium oxide.

2. The method of dehydrogenating gas selected from the group consistingof ethane, propane and butane, which comprises, contacting the gas at adehydrogenating temperature between 350 and 750 C. with a catalystconsisting of activated alumina impregnated with beryllium oxide.

8. The method or dehydrogenatlng dehydrogenatable hydrocarbonscomprising, contacting said hydrocarbons at temperatures ofapproximately 350 to 750 C., with a catalyst prepared by impregnatingactivated alumina with a solution of beryllium nitrate, drying theresulting mixture and heating in contact with air to an elevatedtemperature not in excess of 800 C., sufllcient to form beryllium oxide.

CARHSLE M. THACKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

